Various examples show a certain difference (3)
I believe the answer is:
sex
'a certain difference' is the definition.
The answer and definition can be both human attributes as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'various examples show' is the wordplay.
'show' indicates the answer is hidden within the clue.
'SEX' is hidden in the letters of 'various examples'.
Can you help me to learn more?
(Other definitions for sex that I've seen before include "Gender" , "Expert in the treatment of coital problems" , "VI (Lat.); m. or f." , "Hanky-panky" , "Male or female" .)